Research turns theories about superconductivity temperature on their head

The IBS Centre for Correlated Electron Systems (CCES) has revised existing theories to explain the working mechanism of iron-based superconductors.

Superconductors are a relatively new concept; they were brought to prominence in the late 1980s when two Nobel Prize winners discovered a new superconducting material. The basic principle of superconductivity arises when a superconducting material is cooled to a fairly low critical temperature allowing an electric current to flow without resistance.

The Nobel Prize winners reported their superconducting material — oxides which contain copper and rare earth metals — becomes a superconducting material below -250°C, higher than the previous temperature of -269°C. This led to a boom in developing similar materials for commercial use. Today, research has moved on greatly; oxides are replaced with iron-based superconductors which are cheaper to mass produce and also permit a current to flow unabated.

To understand the working mechanism of iron-based superconductors, scientists have to significantly raise the transition temperatures to source the reason for the increase. Many researchers initially work on the assumption that the nesting effect is a dominant factor, especially in the case of pnictide superconductors [PSD]. Later, scientists discovered another type of superconductor, chalcogenide superconductors [CSD]. Since it turned out that CSD is not subject to the nesting effect, the discovery of CSD generated controversy on the mechanism of their superconductivity. The nesting effect states when the surface temperature is increased, electrons become unstable thereby altering their properties both electrically and magnetically, allowing conductors to turn into superconductors.

Working under the assumption that a strong nesting effect in PSD corresponds to high temperature, the CCES team used potassium (K) and sodium (Na), two alkaline metals with peripheral electrons, thereby facilitating an easy transfer of electrons to other metals. They heated K and Na in a vacuumed environment to excite their atoms whereby the atoms attached to the surface of PSD, which have a lower temperature than the K and Na. As a result, electron doping took place on the surface of PSD. The IBS team measured the momentum and kinetic energy of electrons and revealed, for the first time, that there is, in fact, no correlation between superconducting transition temperature and the nesting effect in PSD as is the case in CSD.

“Up to now the prevailing theory of PSD and CSD have been thought of as two different systems. Our research is a starting point to confirm that those two superconductors have the same working mechanism. We have laid a cornerstone for the discovery of iron-based superconductors, whose production cost is low and has no restraints in its current,” said CCES Associate Director Kim Chang Young.

The research was published in the journal Nature Materials.